Northwest Africa 2402 (NWA 2402)

(Northwest Africa)

Purchased: May 2017

Classification: Lunar meteorite

History: The meteorite was exported from Morocco to Tucson where it was purchased by N. Gessler.

Physical characteristics: Weathered reddish-black fusion crust on one side. Dark-gray matrix with abundant clasts, frequently angular in outline, up to 8 mm, varying from white to near-black.

Petrography: The texture is an immature regolith breccia, gradational with polymict nonregolithic (fragmental) breccia. A finite but very sparse abundance of regolithic spheroids (two identified in a large thin section) is the main indication for an immature regolith breccia. The groundmass is mafic-rich. Clasts vary in mode from Ti-poor basaltic to anorthositic (9/10 plagioclase, granulitic). Pyroxene is the dominant mafic silicate; and in the groundmass, in the basaltic clasts, and in relatively coarse mineral clasts, mostly shows a similar fine, roughly µm-scale, exsolution. Lithic clast textures include vitrophyric, fine-scale poikilitic (impact melt?), granulitic, and medium-grained basaltic. One unusual clast, 0.4 × 0.2 mm, consists of a symplectitic intergrowth of roughly 50% ferroan olivine, 35% silica and 15% augite (with very fine-scale exsolution lamellae of low-Ca pyroxene) and 0.5% ilmenite.

Geochemistry: On the pyroxene quadrilateral, compositions (28 analyses) scatter evenly across the space bounded by Fs₂₂Wo₉, Fs₅₄Wo₆, Fs₅₂Wo₂₁ and Fs₃₈Wo₃₉; the last being the pyroxene of the olivine-silica-pyroxene simplectitic clast. Pyroxene FeO/MnO averages 65.5. The olivine of the sympectitic clast is uniformly Fa_83. Olivine elsewhere is as magnesian as Fa_28. Plagioclase (8 analyses) ranges from An₈₈ to An₉₇, the latter extreme coming from the same poikilitic highland clast that yielded the Fa₂₈ olivine. Two glassy spheroids have VLT-mare compositions similar to glasses in Yamato 793274. The bulk composition, determined by INAA and fused-bead EPMA applied to 2 chips totaling 760 mg, has 18 wt% Al₂O₃, 12.2 wt% FeO and Mg/(Mg+Fe) = 57 mol%, a combination that (along with the spheroids, and the compositional spread and slight exsolution in much of the pyroxene) suggests a significant VLT-mare component. The bulk TiO₂ is only 0.58 wt%. The bulk-rock concentration of the arch incompatible element Th is 1.0 µg/g. Geochemically as well as petrographically, this sample strongly resembles the first highland-mare mixed breccia, Yamato 793274.

Classification: Lunar mixed highland-mare breccia

Specimens: Main mass with Gessler, type specimen at UCLA.